How can i make curve from isovalue ?

Hello,

I have a this fig :

We can clearly see that we have some isovalue curve, but I do'nt know how to draw these curves.

Something like this (made by paint) :

I have 3 vectors volume 315x1 pdw 315x1 cost 315x1

For tool like contour or mesh, you should have the Z (=cost in my case) matrix as 315x315, but it's not my case ...

I hope it's clear for you, thank you a lot for your help.

ps : Sorry for my english ...